11/22/2010 @ 6:00PM

America's Dirtiest Vehicles

Starting in 2011 the Ford Focus electric sedan will be sold in 19 cities across the United States. It’s built in Michigan, uses the same platform as the conventional, gas-powered Focus sedan, and can go 100 miles on a single charge of its zero-emission lithium-ion battery.

Compare that to the Buick Lucerne. The $29,730 sedan gets 15 miles per gallon in the city, and 23 mpg on the highway. All that burnt fuel dumps an EPA-estimated 10.4 tons of carbon dioxide into the environment yearly–significantly more than other cars in its class, like the
Toyota
Avalon (8.1 tons per year) and Chevrolet Impala (6.3 tons).

In fact, the Lucerne is so far behind the pack in terms of its environmental footprint that it landed on our 2010 list of the year’s dirtiest vehicles, along with the GMC Yukon, Cadillac CTS-V and Toyota Sienna.

To be fair, all of these cars meet or exceed federal emissions standards, and are significantly cleaner than the heavy, loud, inefficient gas guzzlers our grandparents drove. Automakers are quick to defend their cleanliness: The Sienna, for instance, rates lower in terms of fuel economy because of a gas-hungry all- wheel-drive model, which competitors don’t offer, according to a Toyota Motors spokesman.

Still, the cars on this list lag behind the rest of the market, and are certainly “dirtier” than other new models.

Behind the Numbers

To determine the dirtiest cars on America’s roads, we looked at data from the U.S. Environmental Protection Agency for all 2011-model-year vehicles. Each car was scored for its performance in terms of air pollution, fuel efficiency and carbon footprint ratings.

Our air pollution score reflects the amount of tailpipe emissions a vehicle releases; vehicles with better scores emit fewer pollutants like hydrocarbon, carbon monoxide and formaldehyde. The carbon footprint score measures the impact a vehicle has on the environment, based on how many tons of CO2 it dumps annually. Those estimates are based on full fuel-cycles, combine all steps in the use of a fuel from production to consumption, and include carbon dioxide, nitrous oxide and methane, the three major greenhouse gases emitted by motor vehicles.

For each car, we supposed 15,000 miles driven annually, 45% on the highway and 55% in the city. The worst offenders in each of 10 automotive segments made our list.

We did not evaluate vehicles classified as “heavy duty,” like the 3500 series of the Dodge Ram, which are exempt from federal fuel economy requirements. We also deliberately omitted some vehicles that rated higher on the particulate-emissions scale, including exotics like the Ferrari 599 GTO and high-performance variants like Mercedes-Benz’s AMG. Many of those cars do have poor emissions and fuel efficiency ratings but are produced in such small quantities and are driven so infrequently that they don’t significantly contribute to air-pollution problems.

“You’ve got to watch out for the assumption that they’re evil because the car happens to have a [poor] rating,” says Lonnie Miller, vice president of marketing and industry analysis for R.L. Polk. “You’ve got to ask yourself, was that the priority of the thing they were making in terms of the car’s definition.”

MPG Matters

Our analysis shows that the biggest factor affecting a car’s “dirtiness” is its fuel efficiency–or lack thereof. A 20-mile-per-gallon gas guzzler creates more pollution as it burns more fuel. Drive a car that gets just 5 miles per gallon more, and you’ll prevent 10 tons of carbon dioxide from hitting the air over a vehicle’s lifetime, according to EPA data.

Vehicular carbon dioxide emissions are a major factor in air pollution. Cars account for 51% of the carbon dioxide emissions in a typical household, while appliances like refrigerators account for 26%, and heating and cooling systems account for 18%. The rest of the spectrum comes from inefficiencies and waste, according to the EPA.

A Few Surprises

All of the vehicles on our list scored equally poor in terms of the amount of air pollution they release. But there are still some vehicles that stand out from the pack, like the Cadillac CTS-V, which boasts the biggest carbon footprint, at 13.3 tons of CO2 emitted each year. This 8-cylinder automatic large sedan gets just 12 mpg in the city and 18 on the highway, with anticipated annual fuel costs of more than $3,300, according to the EPA. As expected, the manual and V6 versions of the CTS receive better scores than the automatic version with a bigger engine.

The Nissan Titan stands out for a different reason: Surprisingly, the version of this truck that runs on conventional gasoline gets better gas mileage than the version that runs on supposedly more eco-friendly E85 biofuel. E85 is perceived as more green because of its smaller carbon footprint (10.6 tons per year vs. 13.3 for regular gasoline).

It’s important to rate and rank vehicle efficiency, says Karl Simon, director of compliance and innovation for the EPA’s Office of Transportation and Air Quality, because it helps consumers make smarter purchases. It also prompts automakers to innovate.

“There’s definitely a secondary benefit to this process,” says Simon. “Nobody wants to be known as the dirty manufacturer.”